1. Field of the Invention The invention relates to wire machinery and more specifically, to an apparatus for manufacturing compact conductors on single or double twist bunchers, twisters or stranders.
2. Description of the Prior Art
Machines sometimes denominated as stranders, twisters, single and double twist twisters, single and double twist stranders, cablers and bunchers have been in existence for many years. These machines are used to combine a plurality of individual wires and bunch or strand them together by imparting a single or double twist to them.
In the case of tubular or rigid stranders, the supply bobbins are mounted inside the rotating section or sections of the machine and the strand is pulled by an outside capstan and wound on a stationary stand. Machines of this nature are shown, for example, in U.S. Pat. No. 4,253,298. These machines have been used to make compact conductors by different methods. One such machine is described in U.S. Pat. No. 4,212,151.
In the case of the other machines mentioned above, which will be referred to as "bunchers", individual strands or wires are typically payed off from a plurality of bobbins and directed at one input end of the buncher, or at both ends of the machine in the case of the buncher described in U.S. patent application No. 602,667, filed 4/23/84 the assignee of the subject application.
The wires are grouped or bunched together at a closing point prior to entry into the machine. The closing point is fixed relative to the main part of the machine.
The bunched wires or strands are then introduced into one end of a bow which rotates about the longitudinal axis of the machine.
In the case of double twist bunchers, it is this rotation of the bow that imparts a first twist to the wires. Leaving the bow at the other end, the bunched and now twisted wires pass over a second exit pulley or sheave which rotates with the bow. From this rotating sheave the bunched or stranded cable is directed over a sheave that is mounted on a cradle that is stationary in relation to the frame of the machine. A second twist is imparted to the wire between the last sheave mounted on the bow and the first sheave attached to the cradle.
Additional pulleys disposed within the space defined by the rotating bow, guide the now double twisted cabled wires to the bobbin supported within the stationary cradle and are wound on the bobbin itself while being evenly distributed thereon. Depending on the machine, slightly different wire guide arrangements have been used.
Double twist bunchers and closers have been extensively used in the electrical wire and cable, steel tire cord and steel rope industries for many years.
Typical machines are illustrated in the "Electrical Wire & Cable Machinery" catalog published by Ceeco Machinery Manufacturing Limited, the assignee of the subject application. Other exemplary structures of existing machines are disclosed in U.S. Pat. Nos. 3,570,234 and 3,732,682.
Machines for twisting a plurality of wires with the single twist system comprise a rotatable flyer and a reciprocally traversing reel rotatably supported within the flyer. A speed differential exists between the rotation of the flyer and the reel.
In order to keep a constant lay, the rotation of the flyer and of the bobbin are controlled in such a way that a constant lay is maintained and a single twist is imparted to the individual wires fed through the flyer and onto the reel. Machines of this kind are described, for example, in U.S. Pat. Nos. 2,817,948 and 4,235,070.
The above machines are normally used to manufacture uncompacted stranded or bunched conductors where the round cross-section of each individual wire is maintained in the final stranded or bunched conductor thereby introducing spaces or interstices between adjacent strands.
In order to maximize the current carrying capacity of conductors with a specified cross-section of the final or stranded cable, or to reduce that cross-section for a specified current carrying capacity, techniques have been developed to reduce the empty spaces in a stranded conductor by pulling a conventionally stranded cable through compacting dies or roller dies. By doing this, each round wire is randomly deformed and compressed against the others resulting in a smaller overall cross-section with the same ampacity rating as the larger non-compacted conductor. This is important, especially when such a stranded cable is subsequently insulated since the amount of insulating material necessary can be substantially reduced and therefore the cost of the overall finished cable is lowered.
Since a large amount of energy is required to force and pull a stranded conductor through a die in order to compact it, this process is usually carried out with tubular or rigid stranders such as those described in the Ceeco Machinery Manufacturing Limited "Electrical Wire & Cable Machinery" catalog, or, for example, in U.S. Pat. No. 4,098,063.
Tubular stranders and rigid stranders are expensive machines and attempts have been made to manufacture compact conductors with single twist and double twist equipment or bunchers. These latter machines are most productive since for similar products they can impart a higher number of twists per minute. However, there are many difficulties in achieving acceptable compact conductor quality and in providing the required pulling forces within the small confines or limited space within the cradle of the machines. In the state-of-the-art double twist machines, all the compacting must take place in the cradle just before the takeup reel. Therefore, prior art double twist machines have to be run at reduced speeds when producing compact conductors' of acceptable quality.
In double twist machines there is a further complication due to the fact that the two twists take place, one at the entry pulley of the bow and the second one at the exit pulley as previously mentioned.
As a consequence of the second twist there is a tendency to shorten the effective length of the other wires relative to the center wire. The result of this action is to distort the wires prior to the compacting device. The state-of-the-art compacting devices overcome this distortion by stretching all the wires in order to produce an acceptable compact conductor. The force exerted on the wires necessary to achieve this objective is considerable, resulting in (a) inefficient use of energy, (b) reduced speed capability, (c) poor product quality, and (d) lower degree of compactness.
Therefore, the state-of-the-art equipment does not produce a compact conductor comparable with those that can be manufactured with more expensive and slower machines such as tubular and rigid stranders where the compaction process can take place outside of the rotating body of the machine and therefore power and/or space factors are of little or no importance.